1. Field of the Invention
The present invention relates to a dust cover for a ball joint.
Further, the present invention relates to a dust cover for a ball joint which is used in an automobile suspension device, and a steering device.
2. Description of the Conventional Art
Conventionally, as a ball joint to which a dust cover is installed for the purpose of a dust prevention and a water prevention in a ball joint coupling portion, there has been known a dust cover for a ball joint which is described in FIG. 5 (Japanese Unexamined Patent Publication No. 62-137408).
In a seal structure of this kind of ball joint dust cover, a spherical head portion 200 formed in one end of a ball stud 100 is retained within a socket 300.
Further, a shaft 400 in the other end of the ball stud 100 is fastened and fixed to a knuckle 500.
On the other hand, a one end large-diameter opening portion 800 having an approximately C-shaped cross sectional shape of a dust cover 600 made of an elastic material is fixed and retained within an annular groove portion 310 which is formed in an outer peripheral surface of the socket 300 by an annular pressure ring 700, and the other end small-diameter opening portion 150 is retained to the shaft 400.
The pressure ring 700 employs a circlip which approximately has a rectangular cross sectional shape.
In this kind of conventional dust cover 600 made of the elastic material, in the case that the ball stud 100 oscillates in a state in which the ball stud 100 is inclined as shown in FIG. 5, a force extending the small-diameter opening portion 150 is applied in a side in which a film portion of the dust cover 600 made of the elastic material extends (a right side on the drawing). Therefore, there is generated a so-called mouth opening phenomenon of the small-diameter portion 150 in which a lip portion of the small-diameter opening portion 150 and the knuckle 500 is disconnected.
As a result, a seal performance in the small-diameter portion 150 is lowered, and a problem that sedimentation or garbage enters into the dust cover 600 from an external portion has been brought about.
Particularly, the rubber constructing the dust cover 600 made of the elastic material loses an elasticity under a low-temperature atmosphere, and a following property of the film portion is lowered in relation to an oscillating motion of the ball joint. As a result, it has been known that the mouth opening phenomenon in which the seal lip portion moves away from the shaft 400 is remarkably generated.
As one of methods for taking measures to the phenomenon, there has been attempts to improve the sealing performance by fitting a retainer having an L-shaped cross section to an outer peripheral surface of the ball stud and closely attaching the dust lip provided in the small-diameter opening portion to the retainer side. However, the mouth opening phenomenon can not be sufficiently resolved.